This invention relates to horizontal belt vacuum filters. Horizontal belt vacuum filters typically comprise a rubber belt that supports a fabric filter web of like width. The belt and the web are held by rollers and moved along an endless path. The belt is provided with channels that underlie the filter cloth and is further provided with holes that communicate with vacuum boxes or pans disposed beneath the upper stretch of belt and web. A feed slurry is uniformly deposited over the full width of the filter by a top feed arrangement. This eliminates cake formation problems associated with fast settling material. Gravity helps reduce vacuum energy requirements and cake formation time. The cake travels with the filter media and dewatering is accomplished by applying suction from the filter boxes through the holes and channels in the rubber belt and the weave of the filter media. Wash liquid is applied to the cake in one or more independent washing zones to optimize product recovery. Filtrate and air enter the vacuum receiver(s) where the liquid drops out and is pumped away. Air exits at the top of the receiver due to negative pressure developed by the vacuum pump. Cake is discharged as the filter media travel around a small roller after separating from the rubber drainage belt. Multiple wash sprays clean the drainage belt and filter media independently to extend the service life of both. Continuous tension is maintained on the belt and the filter media. Sensors control positive automatic tracking and alignment of the filter media.
Horizontal belt vacuum filters can be applied to extract liquids from many different slurries including fibrous materials, fine slimes, and coarse granular materials. The filters can provide high extraction efficiency, low cake moisture, increased production, and reduced operating costs while achieving maximum filtration area in comparison to other filter options.
One area of increasing demand for horizontal belt vacuum filters is in the treatment of oil sands tailings.
Oil sands, also known as tar sands, or extra heavy oil, are a type of bitumen deposit. The sands are naturally occurring mixtures of and or clay, water and an extremely dense and viscous form of petroleum called bitumen. They are found in large amounts in many countries throughout the world, but are found in extremely large quantities in Canada and Venezuela.
Oil sands reserves have only recently been considered to be part of the world's oil reserves, as higher oil prices and new technology enable them to be profitably extracted and upgraded to usable products. Oil sands are often referred to as unconventional oil or crude bitumen, in order to distinguish the bitumen and synthetic oil extracted from oil sands from the free-flowing hydrocarbon mixtures known as crude oil traditionally produced from oil wells.
Oil sands bitumen is utilized for synthetic crude oil (SCO) production by surface mining, bitumen extraction followed by primary (coking) and secondary (catalytic hydrotreating) upgrading processes. SCO is further refined in specially designed or slightly modified conventional refineries into transportation fuels. Oil sands tailings, composed of water, sands, silt, clay and residual bitumen, are produced as a byproduct of the bitumen extraction process. The tailings have poor consolidation and water release characteristics. For over twenty years, significant research has been performed to improve the consolidation and water release characteristics of the tailings. Several processes were developed for the management of oil sands tailings, resulting in different recovered water characteristics, consolidation rates and consolidated solid characteristics. These processes may affect the performance of the overall plant operations.
When oil sands tailings are placed on a horizontal belt filter, bitumen blinds the surface of the cake before all of the free liquid has passed through the cake. If this surface is raked, to rearrange the particulates in the cake and allow for a more thorough extraction of liquid (aqueous) content, the remaining liquid forms another surface film immediately. In the treatment of oil sands tailings, raking generally reduces filter media life inasmuch as the filter cloth becomes quickly clogged with bitumen and fine particulate material